Most of medical X-ray images for use in a diagnosis are images by the absorption contrast method. The absorption contrast method forms a contrast by an attenuation difference in X-ray intensity when an X-ray transmits through a subject. Meanwhile, the phase contrast method is proposed, which obtains the contrast not by the absorption of the X-ray but by a phase change of the X-ray. For example, phase contrast imaging is performed, which obtains an X-ray image with high visibility by edge enhancement using refraction of the X-ray at the time of magnification imaging (for example, refer to Patent Literatures 1 and 2).
The absorption contrast method is effective for imaging of a subject such as a bone, in which the absorption of the X-ray is large. As opposed to this, the phase contrast method is capable of also imaging a mammary tissue, an articular cartilage, and a soft tissue on the periphery of a joint, which have small X-ray absorption differences and are less likely to appear as images by the absorption contrast method, and is expected to be applied to the x-ray image diagnosis.
As a device for the phase contrast imaging, the Talbot interferometer using the Talbot effect is also examined (for example, Patent Literatures 3 to 5). The Talbot effect refers to a phenomenon that, when coherent light transmits through a first grating in which slits are provided in a constant cycle, a grating image of the light is formed in the constant cycle in a traveling direction thereof. This grating image is called a self-image, and the Talbot interferometer arranges a second grating at a position where the self-image is formed, and measures interference fringes generated by slightly shifting the second grating. When an object is arranged in front of the second grating, moire is disturbed. Accordingly, if X-ray imaging is performed by the Talbot interferometer, then the subject is arranged in front of the first grating, a coherent X-ray is irradiated thereonto, and a moire image thus obtained is arithmetically operated, whereby it is possible to obtain a reconstructed image of the subject.
Moreover, a Talbot-Lau interferometer is also proposed, which places a multi-slit between an X-ray source and the first grating, and increases an exposure dose of the X-ray (for example, refer to Patent Literature 6). The conventional Talbot-Lau interferometer is a meter that images a plurality of moire images at a constant cycle interval while moving the first grating or the second grating (while relatively moving both of the gratings), and the multi-slit is provided in order to increase an X-ray dose.
Moreover, in Japanese Patent Application No. 2009-214483 (PCT/JP2010/53978), the applicant of this application has filed a system in the Talbot-Lau interferometer, which enables scanning with good machine accuracy by moving the multi-slit with respect to the first grating and the second grating, and is capable of obtaining a high-definition image. Furthermore, in Japanese Patent Application No. 2010-061993 (PCT/JP2011/053904), the applicant of this application has filed a system in the Talbot-Lau interferometer, which is capable of obtaining the high-definition image.
As a method of creating the reconstructed image from the moire image, a method of creating the reconstructed image from one moire image by using the Fourier transform method is also known (for example, refer to Non-Patent Literature 1), as well as such methods as mentioned above, each of which creates the reconstructed image by the fringe scanning method from the plurality of moire images at the constant cycle interval, which are obtained by the Talbot interferometer or the Talbot-Lau interferometer. In comparison with the reconstructed image obtained by the fringe scanning method, in the reconstructed image obtained by the Fourier transform method, a spatial resolution thereof is inferior; however, the Fourier transform method does not require the plurality of moire images as the fringe scanning method requires. Therefore, reduction of an imaging time can be achieved, and suppression of an influence of a body motion of the subject at intervals among plural times of the imaging can be achieved. Moreover, mechanical operations at the time of the imaging are eliminated, and accordingly, a false image owing to an error of a feeding mechanism for the grating or the multi-slit is also eliminated.
Incidentally, in the case of following up one patient by using the X-ray images, the following operations are frequently performed, which perform the imaging at the same positioning and the same imaging conditions as those for the past image of the patient concerned, and array and display both of such a diagnostic image imaged this time and the past image so that a physician can be facilitated to compare both with each other and interpret the same (for example, refer to Patent Literature 7).
Moreover, at the time of diagnosing the existence of a certain lesion, for example, the existence of a tumor, a cancer, or calcification in the mamma, the following operation is also performed, which arrays and displays a typical case image, a teaching image, a normal image and the like with regard to a suspected lesion together with the X-ray image of the patient as a diagnosis target, and thereby enhances diagnostic accuracy.
An extent to which the diagnostic accuracy is enhanced when a reference image such as the past image and the case image is arranged at a best position with respect to the diagnostic image differs depending on a type of the lesion. Moreover, in some case, the reference image to be taken as a comparison target is plural. In any case, on a display screen, the diagnostic image and the reference image are displayed in parallel while being physically apart from each other. Accordingly, in the case of performing such comparison and interpretation, a line of sight is moved left and right or up and down between the diagnostic image and the reference image, a movement of the line of sight is increased, and this causes a fatigue. Moreover, every time of moving the line of sight between the respective images, the physician must make a diagnosis while paying attention to a positional relationship in region of interest between the images, and this is also a cause of the fatigue.
Accordingly, in order to reduce the movement of the line of sight at the time of the comparison and the interpretation, there is proposed a technology for repeatedly displaying such a comparison target image on a screen of one display means at a display speed ranging from one frame to five frames per second (for example, refer to Patent Literature 8).